Multiple access networks enable network operators to exploit the statistical multiplexing gain arising from a number of users sharing network resources. However, over-allocation of resources can lead to adverse operating conditions, such as unacceptably long delays. The provision of guaranteed Quality of Service (QoS) levels to data flows of higher priority than best effort data flows attempts to address this issue. Without admission control to prevent an overload of the high priority class, however, QoS guarantees cannot be provided or maintained. Thus, prioritized channel access must be coupled with admission control that limits the number of high priority flows.
Wireless Local Area Network (WLAN) technologies have seen an enormous growth in popularity and are currently being deployed in home, office and public access spaces, particularly as the last hop network. The growing popularity of streaming media applications and Voice over Internet Protocol (VoIP) requires such WLAN's to incorporate Quality of Service (QoS) support. QoS support is currently being standardized in the IEEE 802.11 standard for wireless networks. Two mechanisms will be supported, namely a simple, priority-based approach and a more complex, centralized scheduler based approach to be used where tight jitter control is required. Prioritized access to the network is implemented by using differentiated media access (MAC) protocol variables for the different priority flows, such that high priority flows gain access to the network in preference to low priority flows. Wide deployment of this simple mechanism is anticipated.
Admission control has been widely studied in the context of wide area networks such as Asynchronous Transfer Mode (ATM) and internet Protocol (IP) networks. However, such networks operate at high speeds over reliable wired or optical fiber links. At high transmission speeds, admission control can be non-optimally performed by conservatively allocating resources and reserving more bandwidth than is actually necessary to achieve satisfactory levels of QoS.
Wireless networks, on the other hand, have low transmission speeds and dynamic channel characteristics. Data reliability is usually of greater importance than delay and robust transmission link methods, such as forward error correction and automatic repeat request, are necessary. Consequently, results from studies relating to high-speed data networks cannot readily be applied to WLAN's or other networks exhibiting similar characteristics to WLAN's.
It is known in the art to employ an admission control function that uses a measurement-based approach for calculating the load on the network. The function makes admission control decisions on the basis of the calculated load. Admission control is dependent on the presence of a time stamp in each data packet for estimating delays. However, a timestamp is not available in a WLAN unless inserted by an application.